This invention relates to a composition and method for preparing an artificial sea-water to be used for keeping or cultivating animals and plants living in the sea-water.
When one is going to keep or cultivate organisms living in the sea-water, or to investigate, for example, their ecology, it is desirable to use natural sea-water. In recent years, however, because of the spreading environmental pollution of various kinds, it is recognized that many substances that originally were not present are now present in the natural sea-water, and that the proportions of the components of the sea-water may vary. Thus, it is no longer always proper to keep, cultivate or investigate sea-living organisms using such natural sea-water. On the other hand, when sea-living organisms are kept or investigated for a long period of time in a closed environment such as a water tank, there may occur problems, e.g. changes in the pH of the sea-water and development of diseases. Consequently, it is necessary to continually exchange the sea-water in the tank with a fresh supply. However, there are situations in which the collection of the natural sea-water is disturbed due to rough weather or in which it is difficult to obtain the natural seawater due to the remoteness of the location form the sea. In these circumstances, artificial sea-waters whose composition is similar to the natural sea-water have come to be used for handling sea-living organisms instead of the natural sea-water, and such artificial sea-waters are becoming more and more popular.
Natural sea-water contains about 35 g/kg of various inorganic salts. The major elemental composition of inorganic salts in natural sea-water is shown in Table 1 below.
TABLE 1 ______________________________________ Major elemental composition of the natural sea-water Elements g/L ______________________________________ Sodium 8-13 Magnesium 0.9-1.6 Calcium 0.3-0.5 Potassium 0.3-0.5 Chlorine 15-24 Sulfur 0.7-1.2 Bromine 0.04-0.08 Carbon 0.02-0.04 ______________________________________ (Kaiyo Kansoku Shishinsho, p. 145, Ed. by the Weather Agency, Nihon Kaiyo Gakkai, Tokyo, 1990)
Among the above, sulfur occurs mainly in the form of sulfonate ion, and carbon mainly in the form of carbonate ion.
Besides these elements, it is known that the natural sea-water also contains, although as minor element components, metal ions such as lithium, strontium, barium, titanium, molybdenum, tungsten, manganese, iron, cobalt, nickel, copper, zinc and aluminium ions, and ammonium ion as well as anions derived from boron, iodine and fluorine.
Thus, the artificial sea-waters used for keeping sea-living organisms have heretofore been prepared so that they may have a composition as similar as possible to that of the natural sea-water.
Compositions for preparing artificial sea-waters are usually prepared in the form of a powder, granules or liquid, and they are dissolved or diluted with water prior to use. However, such problems have been pointed out that, when used for keeping organisms in a closed environment such as a water tank, the sea-water produced therefrom exhibits an instability in quality, e.g. a rapid change in pH, a shortage of dissolved oxygen and a subtle divergence in specific gravity from the natural sea-water, and, in addition, promotes the to development of diseases.
Among these problems, the most important are changes in pH, which is due to the lack of buffering capacity of the artificial sea-waters, and development of diseases. Thus, the lack of buffering capacity is a factor leading to pH lowering of the artificial sea-waters, which lowering is caused by organic acids and nitrous acid derived from the excreta of the sea-living organisms and remnants of feed drifting in the water. This lowering in the pH causes suppression of the microorganismic breakdown of the excreta and the remnant of feed, and, in addition, leads to the development of diseases. Considering the time and labor as well as economics involved, it is not feasible to frequently exchange the artificial sea-water in response to the changes in quality of the water in order to maintain the rearing environment.
Because the artificial sea-waters so far used have the many problems described above, the inventors have made an attempt to solve these problems and develop a composition for preparing an artificial sea-water more suitably used for keeping, cultivating and investigating sea-living organisms.